1. Field Of The Invention
The present invention relates to a particle detector for use in the detection and measurement of a number of fine particle such as blood cells.
2. Description Of The Prior Art
There are known two kinds of methods of detecting and counting the number of fine particle such as cells, an optical system using laser light and an electronic method using electric conductivity measurement. The latter system is superior to the former system partly because the whole measurement system is inexpensive and partly because the volume of the object of the measurement can be reflected in the result of the measurement.
A blood cell counter is a typical particle counter using the electric conductivity measurement. A summary of the particle counter of the electric conductivity type will be explained hereinafter.
The particle counter of this type comprises two liquid tanks coupled together through a fine aperture and a pair of electrodes connected to the liquid in the liquid tanks. In measurement, the current of the pair of electrodes is measured applying suitable constant DC current or the voltage across the pair of electrodes is measured applying suitable constant DC current to the electrodes while the liquid flows from the first tank to the second tank through the aperture. In this arrangement, the impedance between the pair of electrodes changes every time the particles such as cells pass through the aperture since the impedance depends on the particles present in the interior of and near the aperture, so that the voltage or current measured across the electrodes is changed in a pulsed manner. Therefore, by counting the number of the pulses or by measuring the amplitude of the pulse, the number of or the size of the particles can be measured.
Although the method mentioned above is suitable for measuring the number and density of the particles, it is impossible to isolate every particle and to divide the particles since the particles are discharged external of the tank through a long discharge tube acting as the part of the great capacity tank after the aperture.